This disclosure generally relates to a system and method for protecting large structures, such as low-rise and high-rise buildings, subjected to dynamic forces, such as earthquakes, and winds, and more particularly, for efficiently and economically increasing the capability of such structures to withstand dynamic forces by partially dissipating the input energy from the structural system through usage of dampers.
Supplemental damping has been used for improving the response of building structures subjected to dynamic loadings. Dampers dissipate energy from a structural system by receiving displacement or velocity between two points of a structure. For more effective usage of dampers, designers have amplified the displacements or velocities that activate the dampers through amplification mechanisms or simply by finding installation points that have larger relative displacements or velocities. U.S. Pat. No. 5,934,028A, titled “Toggle linkage seismic isolation structure”, is an example of a magnification mechanism. Increasing the displacement of a damper reduces the force exerted to the damper which reduces the cost for a viscous damper. However, usage of this system has been limited and implementation of the system in practice is expensive. Another invention that amplifies displacements with the addition of a mechanism is disclosed in the U.S. Pat. No. 6,438,905B2, titled “Highly effective seismic energy dissipation apparatus”. This system includes a complex mechanical magnification system that is connected from one end to a point on a beam. The flexibility of the beam can reduce the effectiveness of the system due to its deflection. U.S. Pat. No. 6,397,528B1, titled “Coupled truss systems with damping for seismic protection of buildings”, uses dampers between two vertically braced bays to take advantage of opposite axial deformations in the columns of the middle bay. Therefore the displacement of a damper installed in the inner bay is increased. This system is useful for tall buildings because in low-rise buildings vertical displacement of columns in a braced bay is small and cannot lead to effective usage of dampers. Limitation of usage only at the top of buildings and in combination with other stiff lateral elements such as bracing limits its performance. Another damping system that is aimed for high-rise buildings is disclosed in U.S. Pat. No. 9,163,424B2, titled “Viscous wall coupling damper”. This system uses rotation of the core shear wall that mobilizes the outrigger arms to activate the dampers that are installed between the outrigger walls and columns. It includes complex detailing and can be used only in the outriggers of high-rise buildings. U.S. Pat. No. 6,233,884B1, titled “Method and apparatus to control seismic forces, accelerations, and displacements of structures” proposes separation of the gravity and lateral system with substantial stiffness difference and provides dampers activated by the displacement between the two systems. The separation between the gravity and lateral system is not feasible for most projects.
There is another group of methods that utilize the Base Isolation concept. All of these methods are significantly more expensive than the above-mentioned methods and are only used when importance of the building justifies the high construction and maintenance costs. However, the performance improvements are also significant. Allowance for large displacements above the base isolators can limit the usage of this system in addition to the costs and maintenance requirement of the isolators. US Patent No. 20130118098A1, titled “Negative stiffness device and method” is theoretically an advanced solution. However, the system is complex and requires a budget that is not available for many buildings in high seismic areas.
Review of different damping systems indicates that adjustment of the damping system with the stiffness of the structure is required for the efficiency of a damping system. Moment frames that can perform well with dampers generally consume more structural materials and are usually used when the architectural design does not allow bracing or shear walls. More rigid structures such as shear wall or bracing systems usually do not provide enough movement to activate dampers efficiently and require amplification mechanisms. Negative stiffness device is directly aimed at modification of the stiffness. Therefore an economical structural system for effective usage of dampers may require a suitably modified lateral system.